At present, an Ethernet interface is used as an uplink interface in most broadband access networks and most convergence networks are the networks constructed based on Layer 2 or Layer 3 switches. As shown in FIG. 1, upon accessed by a user, the broadband access device gets connected with a centralized broadband access server (BRAS) or routing device through the convergence network. Usually, an Ethernet switch or a convergence device may be connected to several to dozens of broadband access devices and each broadband access device may be connected to as many as hundreds of user terminals. Therefore, the number of the users accessing the Layer 2 convergence network may be up to tens of thousands. However, the Ethernet switch performs the switch function based on a media access control (MAC) address and a virtual local area network (VLAN), and the Ethernet switches with MAC based forwarding table of 4k, 8k, 32k and 64k are used usually at present. Therefore, the switching table items that an Ethernet switch can accommodate are limited.
With the development of multiple services, a family accessing the network with broadband may have a plurality of service terminals and each terminal has a Layer 2 MAC address. As a result, the capacity of the VLAN and MAC address table items currently supported by the convergence network are unable to satisfy the demand of the service development.
To enable the convergence layer device to satisfy the demand of the service development, a method for performing Layer 3 routing in a broadband access device, such as a digital subscriber line access multiplexer (DSLAM), may be adopted. That is, upon receiving a Layer 2 packet from a user terminal, the broadband access device replaces a source Layer 2 MAC address in the packet with a Layer 3 interface MAC address thereof. In this way, the packet transmitted upward from the broadband access device only carries a Layer 3 interface MAC address of the broadband access device, thereby the demand for the MAC address forwarding table items associated with the convergence device in the network is dramatically decreased.